1. Field of the Invention
The present invention relates to an internal combustion engine variable cam characteristic control apparatus that changes the valve characteristics of one or both of an intake valve and an exhaust valve through the use of a cam by changing the profile of the cam between two lift patterns, and a three-dimensional cam for use in the control apparatus.
2. Description of the Related Art
A variable engine valve driver which suitably controls the engine characteristic by changing the operation angle or the amount of lift of an intake valve or an exhaust valve in accordance with the operating condition of an internal combustion engine is known (disclosed in, for example, U.S. Pat. No. 5,870,984).
This apparatus adopts a three-dimensional cam provided on the camshaft, and adjusts the position of the camshaft in directions of the rotating axis of the camshaft so as to continuously change the cam profile, thereby achieving a proper operation angle and a proper amount of lift.
The aforementioned three-dimensional cam has a cam profile as indicated by the graph in FIG. 34. The valve characteristic of the three-dimensional cam is adjusted by continuously changing the cam profile between a pattern having a small peak of lift and a pattern having a simply increased total amount of lift as indicated by solid lines in the graph of FIG. 34. For an increase in the valve lift (a change from a small-peak pattern to a great-peak pattern), the valve operation angle is expanded forward and rearward, so that the valve opening timing advances and the valve closing timing delays. Conversely, for a decrease in the valve lift (a change from a great-peak pattern to a small-lift pattern), the valve operation angle is reduced so that the valve opening timing delays and the valve closing timing advances.
However, this simple manner of changing the valve characteristic does not have sufficient flexibility to adapt to various characteristic requirements of internal combustion engines and, in some cases, fails to sufficiently contribute to a desired engine performance improvement.
Accordingly, it is an object of the invention to provide a variable valve characteristic control apparatus that achieves a change in the valve characteristic in accordance with a requirement of an internal combustion engine and provide a three-dimensional cam for use in the control apparatus.
To achieve the aforementioned and other objects, a variable valve characteristic control apparatus of an internal combustion engine according to an aspect of the invention includes a cam having a cam profile that varies at least between a first lift pattern and a second lift pattern, and a controller that controls a valve characteristic of at least one of an intake valve and an exhaust valve of the internal combustion engine by adjusting a position of the cam in a direction of a rotating axis of the cam. The first lift pattern and the second lift pattern provide equal amounts of lift at least at a phase within a valve operation angle.
A three-dimensional cam for use for at least one of an intake valve and an exhaust valve of an internal combustion engine has a cam profile that continuously varies between a first lift pattern and a second lift pattern that provides an amount of lift equal to an amount of lift provided by the first lift pattern at least at a phase within a valve operation angle.
Therefore, the three-dimensional cam achieves, for at least one of the intake valve and the exhaust valve, different amounts of lift at a portion of a valve operation angle and equal amounts of lift at another portion of the valve operation angle. That is, within the valve operation angle, there exists a phase where the amount of lift remains unchanged despite a change of the operating cam profile. Therefore, it becomes possible to select a phase where various cam profiles provide equal amounts of lift and set different amounts of lift occurring at the other phases in accordance with the characteristics of the internal combustion engine.
As a result, it becomes possible to realize a suitable valve characteristic in accordance with a requirement of an internal combustion engine. Therefore, further improvements can be achieved in the output performance of the internal combustion engine, the fuel consumption, the combustion stability, and the like.